Semi-slugs, also spelled semislugs, are land

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s whose shells are too small for them to retract into, but not quite

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

. The shell of some semi-slugs may not be easily visible on casual inspection, because the shell may be covered over with the

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

. This is a type of gastropod that is intermediate between a

slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a ...

(without an external shell) and a

land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial gastropod mollusks that have shells (those without shells are known ...

(with a large enough shell to retract completely into). There exist a number of gastropod families that have semi-slugs species.Breure A. S. H. (2010). "The rediscovery of a semi-slug: ''Coloniconcha prima'' Pilsbry, 1933 (Gastropoda, Pleurodontidae) from Hispaniola". ''

Basteria ''Basteria'' is a bimonthly peer-reviewed scientific journal published by the Netherlands Malacological Society, covering research on molluscs. It was established in 1936 and is now published mostly in English. Since 2000, the editor-in-chief has ...

'' 74(4-6): 78-86. There exist about 1,000 species of semi-slugs in comparison to about only 500 species of slugs.Burton D. W. (1982). "How to be sluggish". ''

Tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...

'' 25(2): 48-63
HTM

Examples

Semi-slugs have a worldwide distribution and have evolved in several families; genera include: *

Palearctic The Palearctic or Palaearctic is the largest of the eight biogeographic realms of the Earth. It stretches across all of Eurasia north of the foothills of the Himalayas, and North Africa. The realm consists of several bioregions: the Euro-Sib ...

and

Nearctic The Nearctic realm is one of the eight biogeographic realms constituting the Earth's land surface. The Nearctic realm covers most of North America, including Greenland, Central Florida, and the highlands of Mexico. The parts of North America ...

** family

Parmacellidae Parmacellidae is a family of air-breathing land slugs, terrestrial pulmonate gastropod mollusks within the superfamily Parmacelloidea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005). This family has no subfamilies (accor ...

: ''

Cryptella ''Cryptella'' is a genus of small-shelled slugs in the family Parmacellidae. Species Species in the genus ''Cryptella'' include: * '' Cryptella alegranzae'' Hutterer & Groh, 1991

'' ** family

Vitrinidae Vitrinidae is a family of small, air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Limacoidea (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005). MolluscaBase eds. (2021). MolluscaBase. ...

: ''

Eucobresia ''Eucobresia'' is a genus of air-breathing land snails or semi-slugs, terrestrial pulmonate gastropod mollusks in the family Vitrinidae, the glass snails. Species Species within the genus ''Eucobresia'' include: * ''Eucobresia diaphana'' ( Drapa ...

Semilimax ''Semilimax'' is a genus of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Vitrinidae. Species The genus ''Semilimax'' includes the following species: * '' Semilimax carinthiacus'' (Westerlund, 1886) * ' ...

, Vitrina, Vitrinobrachium'' * Asia - Pacific ** family Ariophantidae: ''

Parmarion ''Parmarion'' is a genus of air-breathing land semi-slugs, terrestrial pulmonate gastropod mollusks in the family Ariophantidae. ''Parmarion'' is the type genus of the Parmarioninae, which is a synonym of Ostracolethinae. Species of snails withi ...

'', '' Ratnadvipia, Varadia'' ** family Helicarionidae: '' Attenborougharion'', ''

Helicarion ''Helicarion'' is a genus of air-breathing land snails or semislugs, terrestrial pulmonate gastropod mollusks in the family Helicarionidae. MolluscaBase eds. (2021). MolluscaBase. Helicarion Férussac, 1821. Accessed through: World Register ...

'', ''

Howearion ''Howearion'' is a genus of two species of helicarionid semislugs that are endemic to Australia’s Lord Howe Island in the Tasman Sea The Tasman Sea ( Māori: ''Te Tai-o-Rēhua'', ) is a marginal sea of the South Pacific Ocean, situat ...

'', ''

Ibycus Ibycus (; grc-gre, Ἴβυκος; ) was an Ancient Greek lyric poet, a citizen of Rhegium in Magna Graecia, probably active at Samos during the reign of the tyrant Polycrates and numbered by the scholars of Hellenistic Alexandria in the cano ...

'', ''

Parmellops ''Parmellops'' is a genus of two species of semislugs that are endemic to Australia's Lord Howe Island in the Tasman Sea The Tasman Sea ( Māori: ''Te Tai-o-Rēhua'', ) is a marginal sea of the South Pacific Ocean, situated between Aus ...

'', '' Ubiquitarion'' ** Semi-slugs also exist but are exceptional in the

Camaenidae Camaenidae is a family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Helicoidea, the typical snails and their allies. This is one of the most diverse families in the clade Stylommatophora. Th ...

. *

Neotropics The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In bioge ...

** family

Amphibulimidae Amphibulimidae is a taxonomic family of land snails, semi-slugs, terrestrial pulmonate gastropod molluscs in the superfamily Orthalicoidea.Breure A. S. H. & Romero P. (2012). "Support and surprises: molecular phylogeny of the land snail superf ...

: '' Amphibulima'', '' Gaeotis'' ** family Xanthonychidae: '' Cryptostrakon'', '' Semiconchula,'' '' Xanthonyx'' ** family

Pleurodontidae Pleurodontidae is a family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Helicoidea. MolluscaBase eds. (2020). MolluscaBase. Pleurodontidae Ihering, 1912. Accessed through: World Register of Marine Sp ...

: ''

Coloniconcha prima ''Coloniconcha prima'' is a species of air-breathing semi-slug, a terrestrial pulmonate gastropod mollusk in the family Pleurodontidae.Breure A. S. H. (2010). "The rediscovery of a semi-slug: ''Coloniconcha prima'' Pilsbry, 1933 (Gastropoda, Pl ...

'' * Tropical Africa ** family Urocyclidae: '' Gymnarion''

References

{{reflist Gastropod anatomy

Examples

See also

References